Color television display system



March 29, 1960 s. YANDo COLOR TELEVISION DISPLAY SYSTEM 4 Sheets-Sheet 1Original Filed Aug. 25, 1955 NDI-m STEPHEN YANDO BY QR ATTORNEY March29, 1960 s. YANDo COLOR TELEVISION DISPLAY SYSTEM 4 Sheets-Sheet 2Original Filed Aug. 25, 1955 mJmEm OF ATTOR N EY LIJ i...

March 29, 1960 s. YANDO COLOR TELEVISION DISPLAY SYSTEM Original FiledAug. 25, 1955 4 Sheets-Shea?I 3 mmJDa March 29, 1960 s. YANDo COLORTELEVISION DISPLAY SYSTEM 4 Sheets-Sheet 4 Original Filed Aug. 25, 1955STE PHEN YANDO BY Q QR ATTORNEY CGLOR TELEVISION DiSPLAY SYSTEM StephenYando, Huntington, N Y., assigner, by mesne assignments, to SylvaniaElectric Products Inc., Wilmington, Del., a corporation of DelawareOriginal application August 25, 1955, Serial No. 530,599. Divided andthis application March 17, 1958, Serial No. 725,770 l 6 Claims. (Cl.328-124) My invention is directed toward television receivers andcathode ray tube registration systems for use therein. This applicationis a division of application Serial No. 530,509, filed August 25, 1955.

One type of cathode ray tube adapted for use in color televisionreceivers is provided with an image forming screen having a plurality ofparallel stripes, usually vertical stripes, of luminescent material.These stripes are normally arranged in laterally displaced colortriplets, each triplet being composed of three phosphor stripes whichrespond to electron irradiation to produce light ofthe diiierent primarycolors. The stripes are normally scanned horizontally by an electronbeamA which is intensity modulated in accordance with an incoming de'--modulated video signal carrying three signal components; each onerepresenting one of the primary colors. These components are amplitudemodulated and are displaced in phase. In order to obtain accurate colorrendition, at Ithe instant 4the beam strikes any particular colorstripe, it must be intensity modulated by the' corresponding colorsignal component and no other. This action can be accomplished quitereadily through sequentially sampling each color component iny turn, ifthe scanning velocity is held constant. However, the scanningvelocity isnormally not constant, due in part to non-linearities 4in the beamdeflection circuits, and, for example, nonuniformities in the colortriplet distribution onsthe screen surface. Consequently, thesimplearrangement. described above is not practicable; the sampling andscanning opL erations would not be synchronized and the color renditionwould be unacceptable. v It has been proposed to place a plurality ofindexing stripes at equidistantly spaced' intervals on4 thescrcen. Theseindexing stripes may coincide with a particular color stripe in eachtriplet, or can he immediately adja'- cent each triplet; however, thesestripes are composed of ai' material having secondary Vemissionproperties which diler from the secondary emissive properties of thecolor stripes. Thus, when a. horizontal raster is' scanned, the'vresultant secondary emission from the indexing 'stripes provides asource of indexing signals which are pulse-like in nature and which areindicative of the instantaneous position of the electron beam upon thescreen. These signals can then be used to control the beam scanningcircuits in such manner that the velocity of scan'is held constan-t. l

rPhis proposed arrangement suffers from a number of seriousdisadvantages. in the iirst place,k the horizontal deflection generatornecessarily provided in the horizon tal scanning circuit must beextremely complex, expensive and ineii'icient. Moreover, even the besthorizontal -deiiection generator of this type permit-some vvariations inthe scanning velocity and, as a result, the

color rendition is impaired. Moreover,the:corrective action initiated bythe indexing signal is relatively slow, being subject to inherentfrequency dependentdelays in signal transmission, and when the scanning;velocity is varied at aI rapid' rate, thecorrcctive action is delayed infthe manner indicated, and again the colorrenditon is impaired.

.tube of the character indicated wherein the rate of sarn- .pling theincoming color components is cont-rolled in `accordance with theinherent variations in scanning velocity.

Yet another object is to improve the color rendition properties of colortelevision receiver systems utilizing a cathode ray tube characterizedby inherent variation in scanning velocity by controlling the rate ofsampling the incoming color components in. accordance withy thesevariations, said control being affected through the use of variable timedelay networks.

These and other objects of the invention will either be explained orwill become'apparent hereinafter.

In my invention, the indexing signals are used to control .the rate atwhich the color signal components are sampled, and, as the scanningvelocity varies, the sampling rate is likewise varied in synchronismtherewith. As a result, color rendition errors no longer present aproblem.

The indexing signals are not supplied directly to the apparatus (thesampler) in which the sampling operation is initiated; if this approachwere to be used, the inherent frequencyy sensitive delays in theindexing signalV transmission path would introduce phase errors whichresult in intolerable errors in color rendition.

Instead, the indexing signals produced as any one line is scanned in thecathode ray tube are retained within a variable time delay network as,for example, stored in proper time relation within the network orpropagated within the network at a rate insuiciently high to permitcomplete signal passage through the network during the line scanninginterval; these retained signals are then used to control the samplingoperation during the interval in which next succeeding line is scanned.Stated diierently,V the rate of color sampling for any one line iscontrolled inaccordance with the pattern Vof. scanningvelocity'variation established by the immediately preced- Y ingv line.Since there is lessentially no difference between the patterns ofscanning velocity variations for any two adjacentc lines (due to theextremely high degree of line to line stability of any conventionalscanning circuit), this approach results in unimpaired colorrendition.,l

The scanning operation, as is conventional, is initiated by the arrivalof a horizontal line synchronization pulse. Each synchronizing pulse-must travel through a delay'line before being supplied to the scanningcircuits.y lFurther each synchronizing pulse, undelayed, is supplied tothe variable time delay network to cause the retained indexing signalsto be supplied to the sampler. The time delay introduced by the delayline is adjustedl to be equal to the delay required to complete theindexing signal retaining operation so that the scanning operation forone line 'is properly synchronized with the sampling rate determined bythe pattern of scanning velocity variation established bythe immediatelypreceding line.

l Consequently, each synchronizing pulse. initiates: both described withreference to the accompanying drawings wherein:

Fig. l is a simpliiied block diagram of one embodiment of my invention;

Fig. 2 is a diagram of one type of variable time delay network suitablefor use in my invention;

Fig. 3 is a diagram of a second type of variable time delay network andsuitable for use in my invention, and

Fig. 4 illustrates a second embodiment of my invention.

Referring now to Fig. 1, there is provided a conventional cathode raytube identied generally at 1 and provided with an electron gun assembly2 for producing an electron beam, a control grid 3 for said beam, a beamfocus coil 4, and a beam deflection yoke 5. Deflection yoke 5 isconnected to conventional beam scanning circuits (shown in block form at20) which exhibit an inherent variation in scanning velocity, forexample, on the order of i5% about the nominal scanning velocity.

The inner wall of the cone portion of tube 1 is coated with a conductivecoating 6 connection in conventional manner to a point of high positivepotential. This coating terminates at a region spaced from the faceplate 8. Face plate 3 is provided with an image forming screen 9. Screen9 includes a plurality of laterally displaced color triplets, eachtriplet being composed of three different phosphor stripes which, whenirradiated by the electron beam, luoresce to produce light of the threeprimary colors, for example, red, green and blue respectively. Thesestripes are covered with a layer of aluminum or similar material.Arranged over each green stripe is an indexing stripe consisting ofmaterial having a secondary emission characteristic detectably differentfrom the material of the aluminized layer. (This tube is of known typeand is described in detail, for example, in U.S. Patent 2,673,890.Further details on the tube and screen will be found therein.)

Interposed between the coating 6 and the face plate 8 in the inner wallof the tube is a signal pick-ot loop 7 consisting, for example, of aring-shaped conducting coat'- mg or a coil loop inductively coupled tothe tube. The output terminal 10 of the loop is coupled through a delayline 19 to a variable time delay device 11. The output of device 11 isdirectly connected to the conditioning electrode of gate 12, and is alsoconnected through delay line 13 and delay line 14 to the conditioningelectrodes of gates 15 and 16 respectively. The output of all threegates are connected in common to the control grid 3 of tube 1. Thesegates are normally closed.

Three separate received signals respectively indicative of the green,blue and red components of a televised scene, produced in conventionalmanner, are supplied to the inputs of gates 12, 15 and 16 respectively.These signals are then sampled in predetermined order in the mannerdescribed in more detail below to form, at the common output of all thegates, a single signal whose amplitude successively is proportional tointensity of each of the three components. This signal s supplied to thecontrol grid of the tube 1 to control the beam intensity.

Horizontal line synchronizing pulses appear at terminal 17 and are'supplied through delay line 18 to the scanning circuit 20 to initiateeach horizontal scanning operation. These pulses are also supplied to acontrol input 20 of network 11. These synchronizing pulses are producedin known manner, and, therefore, the circuitry for producing thesepulses is not described here.

-When the signal for gates 12, 15 and 16 is supplied tothe control gridof tube 1 and a horizontal synchronizing pulse is supplied to thescanning circuits, a horizontal scanning operation is initiated. Theelectron beam then impinges successively on the aluminized coating andthe indexing stripes of the screen 9, thus producing indexing pulses orsignals which are induced in the pick off loop 7. (Of course, the colorimage is produced on the screen at the same time.) These indexingsignals are fed through delay line 19 to device 11 and are retained inproper time relation therein, so that, at the end of any horizontal linescanning operation, all indexing signals produced during this operationremain in device 11. Upon the arrival of any horizontal synchronizingpulse, these signals are released or read out of device 11 at this sametime relation and are supplied to gates 12, 15 and 16.

Each time an indexing signal is supplied to these gates, gate 12 opensimmediately for the interval in which the signal is present; aftersuitable delay introduced by line 13, gate 15 opens for a second likeinterval, and after an additional delay introduced by line 14, gate 16opens for a third like interval. Only one gate is opened at a time.

Thus, as the electron beam traverses a green stripe, an indexing signalopens gate 12 and the green color component is supplied to the tube.Delay lines 13 and 14 delay the opening of gates 15 and 16 until thebeam traverses the next adjacent blue stripe and red striperespectively.

As indicated previously, a horizontal synchronizing pulse whichidentities the start of one horizontal line, through action of delayline 18, is supplied to the scanning circuits to initiate a horizontalscanning operation in synchronism with the color sampling operationinitiated by the indexing signals stored in device 11.

Since there is essentially no difference between the patterns ofscanning velocity variations for any two adjacent lines, the rate ofcolor sampling is controlled and synchronized with the scanning velocityvariations in the manner previously indicated and accurate colorrendition is obtained.

It will be apparent that the indexing signals produced during anyscanning operation are read in and released or read out of network 11under the control of the synchronizing pulses. Stated differently, thehorizontal synchronizing pulse initiates one scanning operation and thusinitiates the read in operation, while at the same time, this pulseinitiates the read out operation. Hence, any variation or noise jitterin the synchronizing pulses can have no adverse effect; the scanning andsampling operations must remain in synchronism regardless of suchvariation or jitter.

When said jitter exists, the time delay between adjacent scanningoperations can vary somewhat and as a result, the retention time for theindexing signals can likewise vary. Hence, device 11 functions as avariable time delay network, for the indexing signals travelingtherethrough are delayed for a fixed period equal to somewhat less thanone line interval (which is quite small for an additional variableinterval (which is quite small as compared to the line interval) whichis a function of whatever synchronizing pulse jitter or similar effectis present.

One type of variable time delay network which functions in this manneris shown in Fig. 2. It comprises two storage tubes and 101, eight gates102, 103, 104, 105, 106, 107, 108 and 109, one D1 delay line 110, two D2delay lines 111 and 112, one (D14-D2) delay line 113, and a bi-stablemultivibrator or flip-hop 114.

Incoming horizontal synchronization pulses appear at terminal 17 and aresupplied through D2 delay line 111 to the scanning circuit of thecathode ray tube. These pulses are also supplied directly to the inputsof gates 102 and 103 and are supplied through the (D14-D2) delay line113 to the inputs of gates 104 and 105. The outputs of gates 102 and 105are coupled to the scan control input 115 of storage tube 101. Theoutputs of gates 103 and 104 are coupled to the scan control input 116of storage tube 100.

The indexing signals produced at the cathode ray tube (not shown in Fig.2) are supplied through D1 delay line to the inputs of gates 106 and107. 'Ihe outputs of 4gates 106 and 107 are respectively coupled to thesans writling inputs 117 and 118 of tubes 100 and 101 respective y.

The read out outputs 119 and 120 of tubes 100 and 101 are coupled to theinputs of gates 108 and 109 respectively. The outputs of these gates arecoupled together through D2 delay line 112 to terminal 121. Termnal 121is connected to the sampler (not shown in Fig. 2)..

The conditioning electrodes of gates 102,v 104 106, and 109 are coupledto an output 122 of ip-tlop 114. The conditioning electrodes of gates103, 105, 107, and 108 are coupled to the second output 123 of thisflip-hop. Horizontal synchronizing pulses are supplied` to the input ofthe Hip-flop; under the inuence of successive pulses, the flip-hop isurged into one or the other of its two mutually exclusive states.

For example, when the rst pulse is received, the tiipop 114 attains onestate, and gates 102, 104, 106, and 109 are opened while gates 103, 105,107 and 108 are closed. When the next pulse is received this operationis reversed.

Storage tubes 100 and 101V are of a conventional type well known to theart, and are not described in detail here.- Further details, forexample, can be found in June 1955, RCA Review, pp. 197-215, TheRadechon,

or can also be found in U.S. P atent.2,579,629. This patent showsstorage tubes with individual writinginput electrodes and read outelectrodes and a separate vscan control or sweep circuit coupled todeflection plates of the storage tubes. Since my invention is notconcerned with the storage tube and scan control circuitry per se, Ihave shown each tube and associated scan control circuitry in the formof an overall block diagram. These two tubes act together, the storedindexing pulses previously produced during one line scanning operationbeing read out of one tube While the next adjacent line is being scannedand the indexing pulses thusy produced are being stored in the othertube. i

The network shown in Fig. 2 operates in the following fashion. Ahorizontal synchronizing pulse appears at terminal 17 and is suppliedwith D2 delay to the scanning circuits of the cathode ray tube. Thispulse also is supplied to the flip-flop and as a result for example,gates 102., 104, 106, and 109 are opened Iwhile gates 103, 105, 107 and108 are closed.

The gating action is sufficiently rapid so that at least a major portionof this pulse passes without delay through gate 102 to initiate the readout operation of tube 120. 'I'he indexing signals previously stored intube 120 therefore are read out and pass through gate 109 and arrivewith D2 delay at the sampler. Consequently, the scanning action of thecathode ray tube and the color sampling action are synchronized in themanner'l previously indicated.

The same horizontal synchronization pulse previously referred to passeswith D1-l-D2 delay through gate 104 to initiate the Writing or storageoperation of tube 100. The indexing signals producing during the cathoderay tube scanning operation pass with Dl delay through gate 106 and anestored in tube 100.

Upon the arrival of the next horizontal synchronizing pulse, the gateswitching action is reversed and tube 100 is read out while tube 101provides indexing signal storage.

Fig. 3 shows a second type of variable delay network. There is provideda sawtooth generator 150, a clamping circuit 151 coupled to the outputof generator 150, and a plurality of gates, in this example, three gates152, 153 and 154, having their conditioning electrodes coupled to theoutput of the clamping circuit. In addition, there is a signal delayline 155 provided with a plurality of taps in this example, taps 156,157 and 158 connected to corresponding inputs of gates 152, 153 and 154.The outputs of all gates are coupled together to the input of D2 delayline 112. The output of delay line 112 is coupled toterminal 121. Theindexing' signals are. supplied through Dl delay line. to the. input of4delay line 155i The indexing signals are supplied through D1 delaylineY to the input of delay line155. Y

The. indexing signals. are supplied tothe input of delay line 155andpropagate therethrough at axed velocity. The electrical length of theline 15S is so selected that these signals cannot propagate all the wayythrough the line in the time interval ydefined by the. time separationbetween adjacent line synchronizing pulses, even though this intervalvaries in accordance with pulse jitter' or posi'- tion shifts. Theposition of the taps in so selected that the propagating signals must atleast pass tap y156 in the same time interval. Stated differently, thetime separation between adjacent synchonizing pulses can vary, butcircuit considerations will establish certain maximum and minimum timeseparations which cannot be exceeded and the length of the delay lineand the varioustap positions will be. determined in accordance withthese extreme separations.

.'I'he purpose of this arrangement is to insure that, despite variationsin the time separation between adjacent synchonization pulses, theindexing signals will'leave the delay line 155 at an instant such thatthe scanning and sampling operations will remain in synchronism. y

-.To thisend, the sawtooth generator is actuated by each horizontalsynchronizing pulse to produce an Output volttage of sawtooth shapewhich linearly rises in value from 0 to a nal value determined by theclamping circuit. As soon as the output voltage varies from 0 and ahorif zontal synchronizing pulse is supplied to this circuit, thisVclamping action is initiated. Each pulse resets the generator andreturns the outputr voltage tozero. As a result, the value of thegenerator output voltage when clamped is proportional tothe timeseparation between the synchronizingpulse which actuated thegeneratorand the adjacent synchonizing pulse which actuates the clamp 'l gcircuit and determines the final (non-zero) value of the generatoroutput voltage.

This clamped voltagey controls the operations of the gates. Each gate isnormally closed and opens only when the clamped voltage -falls withinpredetermined maximum and minimum voltages.

Thus, if the taps are properly positioned, there will be a range ofclamped output voltages which corresponds to any time separation betweenadjacent synchronizing pulses. Further, if the taps are properlypositioned, the time required for the indexing pulses to propagatethrough the delay line 155 past any of these taps will be equal to acorresponding time sepa-ration. Then if the gate coupled to each tap isconditioned to open only when the clamped output voltage attains a valuewhich is representative of the corresponding time separation, the devicewill function in the desired manner.

Obviously, the number ofgates and taps required depends upon therequirements of the system in which they are used, and normally, morethan three gates and taps would be used.

Referring now to Fig. 4, a cathode ray tube identified at 300 is of thesame general known type shown in Fig. l. However, the tube is providedwith two electron guns 301 and 302 which produce corresponding electronbeams dened as a pilot beam and a writing beam. The writing beam is usedto produce the desired color video display; the pilot beam is used toproduce the indexing signal. Both beams are simultaneously deectedacross the face of the tube and scan the same indexing stripes at thesame time. Control grids 303 and 304 are used to control the intensitiesof the pilot beam and the writing beam respectively. The use of dualbeams prevents undesip able video signal-indexing signal intermodulationand permits easier separation and detection of the indexing signal. f

A pilot oscillator 305 is coupled to the grid 303 to`` 'ff modulate thepilot beam at aniutensty which is insugfl y absopei As a result, duringany cathode ray tube scanning operation, a carrier wave at pilotoscillator frequency pulse modulated by the indexing signals is inducedin the pick-off loop 7. The modulated wave thus induced is fed todemodulator 306 wherein the indexing signals are extracted from themodulated wave. The indexing signals are then fed to the variable timedelay network 11 and operation proceeds thereafter in the same manner asin Fig. 1.

For the purposes of clarity, each element in the drawings other than thevarious delay lines and networks has been described as acting withoutdelay. Obviously, no element acts instantaneously, and consequently eachelement, in addition to its primary circuit function, must act as adelay line, although the amount of delay is extremely small. Therefore,it will be understood that the various delay lines incorporate thedelays of the associated elements as well as the delay of the linesthemselves.

While I have shown and pointed out my invention as applied above, itwill be apparent to those skilled in the art that many modifications canbe made within the scope and sphere of my invention as defined in theclaims which follow.

What is claimed is:

l. In combination with a source of control pulses and a source ofwriting signals, first and second storage tubes, each tube beingprovided with read in, read out and scan control electrodes, first,second and third delay lines, the inputs of said first and third linesbeing respectively coupled to said signal and pulse sources; a firstswitch coupled between the output of said first line and the read interminals of both tubes, said first switch having a first position inwhich the signal source is vcoupled through said rst line to the firsttube read in terminal and a second position in which said signal sourceis coupled through said first line to the second tube read in terminal;a second switch coupled between the output of said third'line, saidpulse source and the scan control electrodes of both tubes, said secondswitch having a first position in which the pulse source is connectedthrough said third line tothe first tube control electrode and isdirectly connected to the second tube control electrode, said secondswitch having a second position in which the pulse source is directlyconnected to the first tube electrode and is connected through the thirdline to the second tube control electrode; and a third switch coupledbetween the read out electrodes of both tubes and the input to saidsecond line, said third switch having a first position in which thesecond tube read out electrode is coupled to said second line and havinga second position in which the first tube read out electrode is coupledto said second line.

2. The combination as set forth in claim 1 further including meanscoupled to said first, second and third switches to place all switchesin a like one of said first and second positions.

3. The combination as set forth in claim 2 wherein said switch coupledmeans is coupled to said pulse source, said means being adapted to shiftall switches together between said first and second positions inaccordance with the arrival of successive control pulses. 4. Thecombination as set forth in claim 3 wherein the sum of the delays ofsaid rst and second delay lines is equal to the delay of said thirddelay line.

5. The combination as set forth in claim 4 wherein said switches areelectronic switches and said switch coupled means is a bi-stablemultivibrator.

6. Thecombination as set forth in claim 5 wherein each electronic switchcomprises at least first and second gates which act in reverse sensewith respect to each other.

References Cited in the file of this patent UNITED STATES PATENTS2,527,632 Graham Oct. 3l, 1950 2,579,269 Mesher Dec. 18, 1951

